1. Field of the Invention
The invention concerns a method of depositing a ferromagnetic thin film onto the surface of a waveguide and a magneto-optic component comprising a waveguide with a ferromagnetic thin deposited by said method.
2. Description of the Prior Art
Magneto-optic isolators are used, among other things, to minimize the reflection of a wave towards its source. "Magneto-optic isolators using the Faraday effect are based on the Faraday rotation principle, i.e. on the rotation of the polarization direction of the wave in a YIG waveguide type component with constant direction saturated magnetization. The process is as follows: the generated wave passes through a polarizer oriented parallel to the polarization of the emitted wave. The wave then passes through the Faraday rotator which rotates its polarization 45.degree.. At the output, the wave passes through an analyzer offset 45.degree. relative to the polarizer. The reflected waves pass through the Faraday rotator in the opposite direction, which rotates the polarization of the reflected waves 45.degree.. The polarization of the reflected waves is then at 90.degree. to the direction of the polarizer (+45.degree. on the outward leg, +45.degree. on the return leg). The reflected waves are therefore stopped by the polarizer and do not affect the source.
To obtain the Faraday effect in the Faraday rotator, the latter must be in a magnetic field parallel to the wave propagation direction. To generate this saturation magnetic field the yttrium-iron-garnet (YIG) core waveguide type component is surrounded by a magnetic film generating sufficient magnetic field in the appropriate direction to magnetize said YIG waveguide type component to the point of saturation in the wave propagation direction.
One method of producing the magnetic film is to grow an SmCo, FeCo or equivalent type polycrystalline film on a substrate favorable to epitaxial growth of the film. The substrate can be GaAs or Al.sub.2 O.sub.3, for example.
In a second step of the process, the resultant film is stripped from its substrate by chemical separation (epitaxial lift-off).
Finally, the separated film is placed on the YIG core waveguide type component to which it adheres by virtue of Van de Waals forces or to which it is glued with a resin.
The number of steps in this method leads to production costs that are ill-suited to mass production of these magneto-optic isolators. Furthermore, the attached film methods require the component that is to receive the film to have an exterior surface of simple geometry. This significantly limits the geometric structures of the waveguides.
Other methods consist of growing the film directly onto the YIG core waveguide type component. However, the external layers of the waveguide type component are made of materials that are much less favorable to epitaxial growth of the epitaxial film than Al.sub.2 O.sub.3 or GaAs. The resulting magnetic field is not uniform in amplitude and/or direction. Magnetization of the magneto-optic guide to the point of saturation is therefore not guaranteed at all points on the guide and the isolation characteristics of the isolator are limited.
One aim of the present invention is to propose a method of depositing a magnetic film directly onto a YIG core waveguide type component in which the crystalline orientation of the film is very significantly improved compared to existing direct deposition methods.